Although millions upon millions of polyethylene bags are used annually, such bags formed of film type plastic are made with rather antiquated techniques. Commonly, the film material used in making plastic bags is supplied in tubular form, known as tube stock, and stored in a large roll.
In all known forms of bag making, the bag material in tube stock is fed intermittently to a sealing and cut-off mechanism, and then the bags are stacked for subsequent handling. As the tube stock is supplied to the cutting and sealing station, the movement of the tube stock is controlled by pinch rollers through which the tube stock is propelled. The pinch rollers revolve to direct an adequate length of stock for the formation of a bag, and then the rollers stop monentarily to allow the necessary sealing and cut-off to be effected, after which the pinch rollers again start turning to supply an additional length of bag material for the next bag to be formed.
In some known machines, the tube stock is laid flat so that the bags are essentially horizontally oriented as they are cut off and sealed; and in other instances, as is disclosed in U.S. Pat. No. 3,192,096, the bag material is initially suspended adjacent the location of the cut-off, and then the bag material is carried by needles to a band sealer for sealing across the ends of the bags while the bags remain in vertical orientation, suspended between conveyor chains.